1. Field of the Invention
The present invention relates to methods for inducing humoral and cellular immune responses against tumor cells and infectious agents. In particular, this invention is directed to methods for stimulating an immune response using an antibody that binds with an epitope of an antigen that is associated with a tumor or an infectious agent, and that contains at least one .alpha.-galactosyl epitope. The present invention also is directed to mutated antibodies that contain at least one .alpha.-galactosyl epitope in an engineered glycosylation site located in the constant region of the heavy chain.
2. Related Art
Transplants performed between phylogenetically disparate species are known to be susceptible to hyperacute rejection which is initiated by binding of xenoreactive natural antibodies to endothelium in the donor organ. Binding of these antibodies activates complement, leading to tissue injury and destruction of the graft. For example, porcine organs transplanted into primates are nearly always rejected within hours. Fukushima et al., Transplantation 57:923 (1994); Pruitt et al., Transplantation 57:363 (1994).
The major xenoantigen responsible for such rejection has recently been identified as a single carbohydrate structure, the .alpha.-galactosyl epitope (Gal.alpha.1-3Gal.beta.1-4GlcNAc-R). Galili et al., J. Exp. Med. 162:573 (1985); Galili et al., Proc. Nat'l Acad. Sci. USA 84:2369 (1987); Galili et al., J. Biol. Chem. 263:17755 (1988). The .alpha.-galactosyl epitope is a glycosidic moiety that is expressed on the surface of cells from most mammalian species excluding humans and other old World primates (catarrhine primates). Expression of the .alpha.-galactosyl epitope is mediated by the .alpha.1, 3galactosyl transferase, an enzyme which is absent in old World primates and humans. In humans, as much as 1% of the total serum IgG is specific for the .alpha.-galactosyl epitope. Galili et al., J. Exp. Med. 160:1519 (1984); Avila et al., J. Immunol. 142:2828 (1989). Significant levels of anti-.alpha.-galactosyl ("anti-Gal") IgM and IgA have also been reported.
Recently, LaTemple et al., Cancer Res. 56:3069 (1996), reported their studies on conferring xenograft characteristics to human cells by ex vivo treatment of tumor cells with neuraminidase and recombinant .alpha.1,3galactosyl transferase. The reaction converts the sialylated N-acetyllactosamine found on the human cell surface carbohydrate moieties into the .alpha.-galactosyl epitope. Tumor cells armed with this epitope were reintroduced to the patients. The results indicated that anti-Gal antibodies help opsonize the tumor cells for phagocytosis by professional antigen presenting cells. LaTemple et al. hypothesized that the antigen presenting cells, after ingesting the "armed" tumor cells (tumor vaccines), would present the appropriate tumor-associated antigens (TAAs) to T cells, and that the patient would eventually develop a tumor-specific immunity. The exploitation of the hyperacute rejection mediated by anti-Gal activated complement, however, will require all tumor cells to be "induced" with the .alpha.-galactosyl epitope, and was not and could not be addressed by this approach. Moreover, the vaccines of LaTemple et al. require removal of a patient's tumor cells, in vitro treatment with enzymes to produce the .alpha.-galactosyl epitope, washing and lethal irradiation.
Galili et al., international publication No. WO 95/24924, describe a more general method for enhancing the immune response to an antigen by positioning an .alpha.-galactosyl epitope either on or juxtaposed to the target antigen. According to this method, such a mixture stimulates opsonization by binding anti-Gal to .alpha.-galactosyl epitopes which increases phagocytosis and subsequent processing of the target antigen by the macrophages. This general approach, however, also requires numerous ex vivo steps.
Therefore, the .alpha.-galactosyl epitope has potential as a means to enhance the immune response to a target antigen, but a need exists for a method that does not depend upon extensive in vitro manipulation.